The compound (1α,2β,4β,5α,7β)-7-[(hydroxydi-2-thienylacetyl)oxy]-9,9-dimethyl-3-oxa-9-azoniatricyclo[3.3.1.02,4]nonane-bromide is known from European Patent Application EP 418 716 A1 and has the following chemical structure:

The compound has valuable pharmacological properties and is known by the name tiotropium bromide (BA679). Tiotropium bromide is a highly effective anticholinergic and can therefore provide a therapeutic benefit in the treatment of asthma or COPD (chronic obstructive pulmonary disease).
Tiotropium bromide is preferably administered by inhalation. Suitable inhalable powders packed into appropriate capsules (inhalettes) and administered by corresponding powder inhalers may be used. Alternatively, it may be administered by inhalation using suitable inhalable aerosols. These also include powdered inhalable aerosols which contain, for example, HFA134a, HFA227 or mixtures thereof as propellant gas.
With regard to the inhalative administration of tiotropium bromide, it is essential to provide the active substance in a finely divided (or micronised) form. The active substance preferably has an average particle size of 0.5 to 10 μm, preferably 1 to 6 μm, particularly preferably from 1.5 to 5 μm.
The above-mentioned particle sizes are generally achieved by grinding (so-called micronisation) of the active substance. Since it is important to avoid, as far as possible, any degradation of the active substance of the medicament as a result of the grinding process, in spite of the hard conditions required while the process is taking place, high stability of the active substance vis-á-vis the grinding operation is an absolute necessity. It must be borne in mind that in the course of the grinding process there may in certain circumstances be changes to the solid characteristics of the active substance which may affect the pharmacological properties of the medicament formulation to be administered by inhalation.
Methods of micronising pharmaceutically active substances, including tiotropium bromide, are known per se in the prior art. Thus, for example, WO 03/078429 discloses a method of preparing micronised crystalline tiotropium bromide monohydrate.
The objective of the present invention is to provide a process which allows virtually anhydrous micronised tiotropium bromide that meets the requirements stated hereinbefore to be produced economically.